Download:

Requirements:

Power supply works for microcontroller, (EP)ROM, and any additionally
needed circuitry.

Working clock of the microcontroller.

All address and data bus lines are OK.

Access to the serial interface, connected to a terminal or a PC running
a terminal program.

Automatic baud rate recognition:

After the reset the monitor waits for two characters on the serial line.
The first one is used to find out the baud rate, so its LSBit has to be
"1" e. g. CR. The monitor expects the second character to be CR
to ensure that it found out the correct baud rate. If this condition is
met, the monitor sends:

Welcome to X51 V1.1!
Enter "HE" for help.

By rule of thumb use low baudrates at low clock frequencies and vice versa.